The Hα line of hydrogen is a very powerful tool for the study of the solar chromosphere (plages, flares, prominences). Although it is difficult to derive in a simple way quantitative information, like chromospheric temperature and electron density, because of the very extensive depth of its formation and the very complex mechanism of excitation, Hα has been successfully used to study the chromospheres of active stars (Herbig, 1985). Moreover this diagnostic has proved to be very useful for the study of surface inhomogeneities and transient phenomena like flares in systems of the RS CVn type and other active stars (Bopp, 1981; Bopp et al., 1988; Fraquelli, 1982).

With the aim of investigating the behaviour of chromospheric activity, we have undertaken an extensive monitoring of Hα emission in a selected group of RS CVn binaries (Strassmeier et al., 1988). We report here preliminary results of the observations obtained in 1988–1989.